1. Field of the Invention
The present invention relates to an acoustic amplification device, and more particularly to improvement in characteristics of an acoustic amplification device using a semiconductor element.
2. Background Art
There has come into wide use an audio amplifier which amplifies an acoustic signal output from a sound source device such as a tuner, a CD player, or a portable media player, and drives a speaker. In the related art, an amplifier using a triode has been used as an amplifier that generates natural sound. However, a vacuum tube such as the triode has a problem in that the life is short, and thus an audio amplifier using a semiconductor element such as a bipolar transistor or a field effect transistor has superseded the vacuum audio amplifier. In many cases, the audio amplifier using the semiconductor element is provided with a negative feedback path between a final stage circuit and an initial stage circuit in order to stabilize a bias voltage, reduce distortion components included in an output signal, and the like.
In addition, JP 6-276037A discloses an audio power-amplifier provided with a negative feedback path between a final stage circuit and an initial stage circuit. In addition, JP 2000-349568A discloses an amplification device using a MOSFET which is operated in a triode region. Here, the triode region refers to a region where a relationship between a drain current and a drain-source voltage closely approximates a relationship between a plate current and a plate-cathode voltage in the triode.